Plastic shaping by means of IR heating and direct pellet molding

Plastic shaping was performed by means of the combination of IR heating and pellet softening in a semitransparent open mold. Three commercial thermoplastic materials were employed (acrylonitrile‐butadiene‐styrene, polyethylene, and polypropylene) and process curves were extracted depending on IR lamp power and interaction time. A simple exponential model was defined for the prediction of molded sample thickness and a master curve was built for all the materials. A scale factor was introduced depending on the IR lamp power and not on the material. Besides, the density of molded sample was monitored, obtaining in such conditions density values comparable to typical injection molded ones, even if a very low load was applied during pellet molding (10 N). POLYM. ENG. SCI., 46:896–903, 2006. © 2006 Society of Plastics Engineers     

Optimization of cure kinetics parameter estimation for structural reaction injection molding/resin transfer molding

A numerical method is proposed for polymer kinetic parameter estimation of either Structural Reaction Injection Molding (SRIM) or Resin Transfer Molding (RTM). The method simulates either radial flow or axial flow of reactive resins through a fiber preform inside a mold cavity. This method considers a non‐isothermal environment with different inlet boundary conditions. Based on the molding conditions, this method can find the best values of chemical kinetic parameters by comparing the simulated temperature history and the experimental temperature history. Since the kinetic parameters are estimated with the real molding conditions, the simulations using these parameter values can have better agreement with molding data than those parameters which are obtained from idealized conditions such as Differential Scanning Calorimeter (DSC). The optimization approach was verified by estimating kinetics parameters for RTM data available in the literature. Temperatures predicted by the optimized kinetics parameters are compared with experimental data for two different molding conditions: injection of a thermally activated resin into a radial mold under constant pressure flow, and injection of a mix activated resin into a radial mold under constant volume. In both cases, the optimized kinetics parameters fit the temperature data well.     

团状模塑料注塑成型"花斑"缺陷分析

本文从材料性能、注塑工艺、模具结构以及真空设备等方面分析了团状模塑料（Bulk Molding Composite简称BMC）注塑成型制品的“花斑”缺陷产生的原因与机理。     

Experimental and analytical procedures for flow dynamics of sheet molding compound (SMC) in compression molding

A package of procedures have been developed to collect and analyze the response of dynamic variables such as pressure, temperature, and mold separation during the compression molding of Sheet Molding Compound (SMC). From the dynamic responses, the molding process was found to consist of two regions: the flow and the subsequent curing reaction region. With an R-25 formulation and a mold closing rate of 30 mm/s, these two regions are well separated and the average flow time is not significantly affected by the maturation time for the material up to 30 days. Several mechanical parameters were estimated based on relatively simple flow models. The relationship between the press force, mold separation, and mold closing rate is found to be sensitive to the restrictions of the flow.     

Key issues in numerical simulation for liquid composite molding processes

Polymer-based composites have a great potential for the manufacture of energy-efficient vehicles. Because of this growing usage and also because mold cost increases with part complexity, numerical simulation of Liquid Composite Molding Processes such as Resin Transfer Molding (RTM) and Structural Reaction Injection Molding (SRIM) are becoming more important. To succeed in that venture, reliable input data as well as a numerical model able to simulate specific molding difficulties and complex shapes must be used. In this paper, several issues are discussed and a computer software is presented. Among them, permeability measurement is discussed. Concerning specific molding difficulties, simulation results compared with experimental data are presented for edge effects, flow in multilayers and flow in ribbed structures. Finally, nonisothermal filling is discussed. Experimental data showing how the temperature boundary layer is developed during the filling of a heated mold are presented.     

Single thermoplastic pellet molding by means of diode laser for micromolding application

An innovative system for thermoplastic micromolding is presented. A completely transparent mold is used, and a diode laser is used as heating source. Laser heating is performed on a single thermoplastic pellet positioned inside the mold between two glass plates. A very low force is necessary for shaping. Molding tests were performed on commercial ABS and several process parameters were investigated such as laser power, interaction time, focalization condition, and support material properties. High pellet formability was observed in all the cases. Using nontransparent pellet supports it is possible to increase molding efficiency even if the risk of polymer degradation increases. A master curve can be fabricated for molding test results providing a correct comparison among the different process conditions. POLYM. ENG. SCI., 47:168–173, 2007. © 2007 Society of Plastics Engineers     

基于CAE的注塑件结构及成型工艺参数优化

应用CAE软件模拟注塑件的成型过程,分析制件潜在的质量缺陷,通过优化制件结构及浇注系统改善了制件成型质量;结合正交试验方法,通过流动＋翘曲分析对模具温度、熔体温度、注射时间、保压压力和保压时间等注塑工艺参数进行优化,获得最佳工艺参数组合,为生产合格制品提供理论依据。     

Experimental investigation of infrared rapid surface heating for injection molding

A low cost and practical infrared rapid surface heating system for injection molding is designed and investigated. The system was designed to assemble on the mold and a control system was used to operate the motion of the lamp holder. Four infrared halogen lamps (1 kW each) were used as the radiative source to heat the surface of mold insert. The temperature increase is verified on the mold plate with a thermal video system. Two types of specular reflectors combined with different bulb configurations were applied to study the heating ability of radiation heating. A modified spiral flow mold was used to test the enhancing filling ability of the rapid surface heating system. Three resins, PP, PMMA and PC were molded in the spiral flow injection molding experiments. If spherical reflector and centralized lamp configuration are used, the temperature at the center of the mold surface is the highest. The temperature of mold center surface is raised from 83°C to 188°C with 15 s of infrared heating. Because the surface temperature of the mold insert is higher than the glass transition temperature of resins before filling, the flow distance of resins in the modified spiral flow mold will be increased. The location effect of the infrared surface heating system on a thin‐long cavity was studied to demonstrate the possibility of using smaller infrared heating area on a large mold surface. A microprobe cavity also demonstrated that with the assistance of infrared heating technology the formability of a microprobe can be greatly improved. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3704–3713, 2006     

Warpage of a large‐sized orthogonal stiffened plate produced by injection molding and injection compression molding

Rectangular plates of the size of 1800 × 600 × 12 mm³ and 1200 × 600 × 12 mm³ were selected for injection molding and injection compression molding, respectively, in order to investigate warpage characteristics of the large‐sized polymer plates with orthogonal stiffener. To determine the mold system and to reduce warpage of the specimen, numerical analyses for injection molding and injection compression molding were performed by using a commercial simulation code. Experiments were performed to verify the suggested mold system and warpage of the specimen. Relatively large warpage of the injection molded product was observed and small warpage of the injection compression molded product was generated. Compression force of the injection compression molding was only 6% of the clamp force of the injection molding. Warpage of the product was reduced significantly by using the injection compression molding. The injection compression molding will be used to substitute expensive and disused wood forms with inexpensive and recyclable polymer plates for concrete casting. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

The effect of injection molding conditions on the mechanical properties of an in situ Composite. I: Polypropylene and a liquid crystalline copolyester based on hydroxynaphthoic acid

In this study, the effect of injection molding conditions on the mechanical properties of polypropylene/liquid crystalline copolyester in situ composites was investigated. Molding conditions such as fill time, mold temperature, and mold thickness were varied to determine the most significant variables that influence mechanical properties. The mechanical property variations were correlated to the shear or extensional stress, which deforms a dispersed phase, and to the Graetz number, which indicates the influence of heat transfer. It was found that higher flexural moduli were obtained in thinner molds and that the maximum mechanical properties for a given mold thickness were obtained near a Graetz number of ten. This indicated that heat transfer was a controlling factor in the formation of in situ composites.     

型腔气体反压智能注射马桶盖模具创新设计

为了解决马桶盖的翘曲变形和表面质量问题,提出一种气体反压注射的方法,通过Moldex3D软件分析预测气体反压工艺塑件存在的可能问题并加以改善.设计了一套气体反压马桶盖模具,利用热流道+冷流道的方式解决了材料浪费和模具偏心问题,采用斜顶+直顶块的联合顶出机构减少了产品变形,同时制定型腔气体反压(GCP)辅助注塑工艺的流程...     

大型塑料件注塑模浇注系统设计

利用模流分析软件Moldflow Plastics Advisers(MPA)对空调机面板注塑模6种构型不同的浇注系统分别进行注射成型流动分析。通过模拟空调机面板在一定成型材料、成型工艺条件下注射成型流动时的温度场、压力场、速度场,获得熔体流动前沿温度、实际注射时间、实际注塑压力、气穴位置、熔接痕位置等参数;在此基础上比较流动结果,预测空调机面板成型质量,确定最优的注塑模浇注系统设计参数,成功地解决了大型塑料件成型时可能出现的充模不足、熔接痕明显等质量缺陷,为模具设计提供了科学依据。     

机器人关节轴螺纹自动脱模注塑模设计

给出了机器人关节轴液压油缸自动脱螺纹的注射模具详细结构,该模具采用点浇口转侧浇口浇注系统,通过采用"液压油缸+齿条+齿轮"的组合传动方式实现螺纹自动脱模,通过采用斜滑块内侧抽芯和外侧抽芯实现成型塑料件的侧向抽芯。通过采用小拉杆、弹簧和限位螺钉的内置定距分型机构保证模具的开模顺序和开模距离。模具在定模板、动模板和斜滑块上均设计了冷却水道。模具成型零件均采用活动式结构,导向定位机构采用12支导柱,成型塑料件最后由推板推出。模具结构复杂,动作繁多,投产后各机构运行顺畅,成型塑料件质量稳定。     

Moldability studies in reactive polymer processing

Reactive polymer processing is the combined polymerization and processing of reactive prepolymers in a single operation. It encompasses a wide variety of processing methods including Reaction Injection Molding (RIM), a relatively new and growing fabrication method. Reaction Injection Molding utilizes impingement mixing of low viscosity fluids, injection of the reactive mixture into a mold, and polymerization therein to enable the molding of large plastic items. Polyurethane is currently the most commercially utilized RIM material although a number of other systems such as epoxy, nylon, and polyester are also suitable. Non-urethane systems such as epoxy are often not as amenable to the process, however, since they are slower reactions and have a potentially damaging exotherm. A comprehensive analysis was developed to determine if a molding system is processable by RIM. Criteria for processability were established and include the ability to mix on impingement, fill large molds characteristic of the process, and provide a short cycle time without promoting a damaging exotherm. The treatment, consisting of both experimental and numerical techniques, was applied to identify potential epoxy molding systems, establish their processing window, and conduct an optimization of the process parameters to evaluate productivity. The analysis and its conclusions are applicable to most reactive polymer processing operations that employ a rapid, exothermic, polymerization reaction.     

Fiber mat deformation in liquid composite molding. I: Experimental analysis

When a resin in injected into the mold in liquid composite molding, the preplaced fiber mat may deform near the inlet gate because of the high momentum carried by the injected fluid. A fiber free region near the gate followed by the fiber mat deformation may emerge. This phenomenon is most likely to occur when the stacked fiber mats have low permeability and the resin has high viscosity. A set of mold filling experiments were carried out using an instrumented metal mold and a small transparent mold to investigate the fiber mat deformation during mold filling. Experimental results showed that the fiber mat deformation was limited to a small region near the gate and that deformation greatly reduced the molding pressure. A forced fiber mat deformation employing a modified gate design was proposed to facilitate mold filling in liquid composite molding.     

团状模塑料（BMC）反射镜注射成型技术的研究

从团状模塑料（BMC）注射成型机、辅助设备、模具、BMC材料及工艺条件,分析BMC注射成型车灯反射镜的技术与要求。     

精密注射成型新技术

介绍精密注射成型的基本特征，说明精密注射成型需具备的几个必要条件，简要介绍注射压缩成型，高速注射成型，无保注射成型，高模温注射成型，超微小精密注射成型，计算机化的注射成型及几种关键控制的注射成型等几种精密注射成型新技术的原理，优点和应用前景。指出先进的伺服驱动技术和计算机智能控制技术的不断发展将为精密注射成型技术提供更为广阔的发展空间。     

The effect of the packing parameters,gate geometry,and mold elasticity on the final dimensions of a molded part

Despite a significant number of publications and the increasing use of numerical simulation, there is still a debate about the optimum gate design and packing conditions in the molding industry. Shrinkage uniformity for unfilled polymers is dominated by the time dependent pressure distribution in the cavity and the resulting volumetric shrinkage; gate freeze-off is obviously important and difficult to predict; and pressure gradients during the packing phase, depend on process and design parameters and are also affected by the mold elasticity. Molding trials have been conducted on an instrumented mold (fan gated rectangular slab, 2 mm thick) under a variety of processing conditions and with different gate thicknesses using HDPE (Solvay Eltex A1050). Pressure decay during the molding cycle at different locations along the flow path have been correlated with sample thickness distribution. Overpacking at moderate packing pressure is shown to be a direct consequence of mold elasticity and to be related to both filling flow rate and gate thickness. The decay to a finite residual pressure can be computed by coupling the mold elasticity with the PVT behavior of the polymer. The results highlight the importance of gate design and processing parameters on the dimensional accuracy of the part and low internal stress level. When dealing with thick gates, packing pressure profiling appears to be the best way to avoid gate area overpacking. Mold elastic deformation can play a significant role in the cavity pressure-time history, even for a seemingly stiff mold construction.